1′,3′,3′-trimethyl-6, 8-dinitrospiro [2H-1-benzopyran-2,2′-indoline]:: Fast thermal enantiomerization and slow thermal equilibration with a ring-opened isomer
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作者:
Kiesswetter, R
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机构:
Univ Regensburg, Dept Organ Chem, D-93040 Regensburg, GermanyUniv Regensburg, Dept Organ Chem, D-93040 Regensburg, Germany
Kiesswetter, R
[1
]
Burgemeister, T
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机构:
Univ Regensburg, Dept Organ Chem, D-93040 Regensburg, GermanyUniv Regensburg, Dept Organ Chem, D-93040 Regensburg, Germany
Burgemeister, T
[1
]
Mannschreck, A
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h-index: 0
机构:
Univ Regensburg, Dept Organ Chem, D-93040 Regensburg, GermanyUniv Regensburg, Dept Organ Chem, D-93040 Regensburg, Germany
Mannschreck, A
[1
]
机构:
[1] Univ Regensburg, Dept Organ Chem, D-93040 Regensburg, Germany
来源:
ENANTIOMER
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1999年
/
4卷
/
3-4期
关键词:
barriers to ring opening;
H-1-NMR temperature-dependent;
H-1-NMR time-dependent;
merocyanine;
spiro-2H-1-benzopyran;
D O I:
暂无
中图分类号:
Q5 [生物化学];
Q7 [分子生物学];
学科分类号:
071010 ;
081704 ;
摘要:
The transformation of the title compound (RS)-2 into the merocyanine 1 was studied by time-dependent H-1-NMR in DMF-D-7 at 22 degrees C. An equilibrium containing 1.9% (RS)-2 is established; the free enthalpy of activation for the (XS)-2 --> 1 process amounts to 101.3 kJ mol(-1). The interconversion of the enantiomers of the title compound was studied by temperature-dependent H-1-NMR in DMF-D-7. The barrier to ring opening (60.1 kJ mol(-1), 23 degrees C) was determined for the first time. Apparently (RS)-2 represents the 2H-1-benzopyran with the lowest Delta G not equal-value for this process which occurs as often as 155 times per second at 23 degrees C. The characterization and all H-1-NMR measurements of (RS)-2 were facilitated by its isolation as a solid. The two reactions, namely interconversion of enantiomers and transformation into a merocyanine, are found to be kinetically independent of each other. Their mechanisms are discussed on the basis of the scheme of free enthalpy changes.